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GEO‘s experience with Signal Recycling

GEO‘s experience with Signal Recycling. Harald Lück Perugia, 22.9.2005. MPR. ~600m. MSR. Dual Recycling in GEO600. Differential arm length: (gravitational wave signal) heterodyne detection S chnupp modulation. Michelson Length Control. Michelson Interferometer. 14.904875 MHz.

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GEO‘s experience with Signal Recycling

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  1. GEO‘s experience with Signal Recycling Harald Lück Perugia, 22.9.2005

  2. MPR ~600m MSR Dual Recycling in GEO600

  3. Differential arm length: • (gravitational wave signal) • heterodyne detection • Schnupp modulation Michelson Length Control Michelson Interferometer 14.904875 MHz 9.017375 MHz • Signal-Recycling control: • separate modulation • frequency • reflected beam from beam splitter AR coating Output Mode Cleaner

  4. SR / PR cavity data ΔL = 93 mm

  5. Problems with SR Error- • Signal: • Small catching range • large influence of MI-deviation from dark fringe. Michelson Length Control Michelson Interferometer 14.904875 MHz 9.017375 MHz Output Mode Cleaner

  6. 2 1 0 -1 -2 Acquisition signal for SRM 2.5 kHz 0 kHz 5 kHz Signal Amplitude [Arb.] SRM tuning [nm]

  7. ~ ~ -C Michelson Length Control Michelson Interferometer 14.904875 MHz 9.017375 MHz Output Mode Cleaner

  8. Amplitude [V/m] Tunable Optical Gain (200-5000Hz)

  9. Tuning of the SR cavity • Tuning is automated using a Labview programme • SR tuning parameters: • SR modulation frequency • SR demodulation phase • SR servo gain • MI demodulation phase • MI servo gain • MI AA servo gain

  10. 119 FSRSR 119 FSRPR 119 FSRSR 119 FSRPR 72 FSRSR 72 FSRPR 72 FSRSR 72 FSRPR 72 FSRSR 72 FSRPR 72 FSRSR 72 FSRPR 119 FSRSR 119 FSRPR 119 FSRSR 119 FSRPR Resonance conditions of Control SBs in SR cavity SR SB MI SB

  11. Amplitude [V/m] Enhanced peak gain @ 1kHz tuning

  12. Dark port contrast / Mode healing Power inside PR cavity increases from PR to DR mode by 40 %. -Ratio of carrier light power at dark port / power incident on beamsplitter ~ 0.05% ~ 1 % < 0.001 % (SB-dominated, 2% MSR) Power rec. MI with therm. compensation Dual rec. MI with therm. compensation Power rec. MI. without therm. compensation

  13. Dual Recycled Performance • Stable locks at desired tuning frequency with durations of up to 121h. • Tuning frequencies 200 – 5000 Hz. • High duty cycle in extended data taking periods ( ~97% during S4, i.e. 4 weeks)

  14. Differential arm length: • (gravitational wave signal) • heterodyne detection • Schnupp modulation P 90° Q 2 EP Quadratures Michelson Interferometer 14.904875 MHz 9.017375 MHz • Signal-Recycling control: • separate modulation • frequency • reflected beam from beam splitter AR coating Output Mode Cleaner

  15. Uncalibrated Michelson Error Points Q P

  16. optical On-line optical TF measurements P and Q CAL actuator

  17. Optical&Electronic Gain

  18. Calibration

  19. Calibrated EP Quadrature Signals h [1/sqrt(Hz)]

  20. Combining hP(t) and hQ(t) • Create filters from noise floor estimates sPP sQQ sPQ h(t) = Pfilter{hP(t)} + Qfilter{hQ(t)}

  21. Combining hP(t) and hQ(t) – results Get the best of hP and hQ plus a little extra! h [1/sqrt(Hz)]

  22. Optical Spring Radiation pressure causes a tuning-dependant force onto cavity mirrors in detuned cavities. The dashed curve shows the radiation pressure on the cavity mirror as a function of the detuning from resonance. The solid curve shows the derivative of the optical force, i.e. the optical spring constant. Positive displacement corresponds to increasing the cavity length. The circulating power on resonance is 60 W. The cavity finesse was 380. The oscillator had a mass of approximately 1.2 g, a measured resonance frequency of 303 Hz, a Q of order 3000 (limited by gas damping), and an inferred mechanical spring constant of 2800 Nm−1. shorter longer From LIGO-P030052-00-R

  23. … Leistungen Optical spring in GEO600 for different intra-cavity powers

  24. … MSR Positionen Optical spring for GEO600 for different MSR positions P=10kW

  25. Summary • tuneable response • mode healing • GW info in both quadratures • more complex SB throughput / noise TFs • optical Spring needs to be taken into account • detailed numeric simulations + understanding • required for advanced detectors

  26. ?Questions?

  27. GEO600 layout (S4 values) T=900ppm 1.5 kW

  28. Mode healing or SB enhancement? • Check which part of the intra cavity power enhancement comes from the control sidebands becoming resonant inside the SR cavity • We get an enhancement of intracav power between PR and SR350Hz of 3.4/2.4 a.u. • Sideband power inside SR? Behind MSR say 50mW -> 2W in front, so the resonant sidebands do not contribute to the power enhancement

  29. Theoretical Noise budget

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